1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, which includes a process of forming a thin film on a substrate, and a substrate processing apparatus.
2. Description of the Prior Art
A flash memory includes an electron accumulation region (floating gate) surrounded by an insulation film, and its operation principle is to perform a data write operation by exchange of electrons through a thin tunnel oxide film and to retain the electrons and keep memorized data for a long time by using insulation property of the thin tunnel oxide film. Even though no operation from the outside is performed, data stored in a flash memory may need to be retained as long as ten years, and a requirement for an insulation film surrounding a charge accumulation region, called a floating gate, is strict. In an interlayer dielectric film disposed between the floating gate and a control gate designed to control a memory cell operation, a stacked structure of oxide film (SiO2)/nitride film (Si3N4)/oxide film (SiO2), generally called ONO, is used and it is expected to have a high leakage current characteristic.
Conventionally, the formation of an SiO2 insulation film in an ONO stacked structure has been performed at a high temperature around 800° C. through a Chemical Vapor Deposition (CVD) process by using an SiH2Cl2 gas and an N2O gas. However, since the device is further scaled down and the capacity of the nitride film among the ONO stacked films is lowered, the adoption of a high dielectric constant film instead of the nitride film has been considered in order for ensuring capacity. To suppress crystallization of the high dielectric constant film, it is necessary to form an SiO2 insulation film formed on the high dielectric constant film at a temperature lower than a forming temperature of the high dielectric constant film.
In the case of forming the SiO2 insulation film, as its forming temperature is lowered, atoms other than silicon (Si) and oxygen (O) contained in a source used for film formation may remain as impurities within the film. Hence, in the case of forming the SiO2 insulation film at a low temperature by using an organic source gas, there has been a problem that carbon (C), hydrogen (H), nitrogen (N) and so on contained in organic source gas molecules remain as impurities within the SiO2 insulation layer.
In addition, in the case of using an inorganic source gas, there has been a problem that hydrogen (H), chlorine (Cl) and so on contained in a source remain as impurities within the film. Since such impurities significantly degrade the film quality of the formed insulation film, there is a need for a technology that can form a high-quality insulation film having a low within-film impurity concentration at a low temperature.